Method for the commercial rectification of a mixture of components



N v. 195a G. s. CREWSQN ET AL 2,724,640

METHOD FOR THE COMMERCIAL RECTIFICATION OF A MIXTURE OF COMPONENTS Filed Nov. 28. 1947 3 Sheets-Sheet 1 Zone jmperafw'v "45/21 0 in Liyu dpfiase .3 11, o in Sa/id P/mse 28 33 96.8 99-0 26 993 "5% Mu r E- 9. j W

INVEN TOR.

N v- 1955 G. G. CREWSON ET AL 2,724,640

METHOD FOR THE COMMERCIAL RECTIFICATION OF A MIXTURE OF COMPONENTS Filed Nov. 28, 1947 3 Sheets-Sheet 2 Z one Emperafure- C.

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Nov. 22, 1955 Filed Nov. 28, 1947 G. METHOD FOR T G. CREWSON ET AL HE COMMERCIAL RECTIFICATION OF A MIXTURE OF COMPONENTS 3 Sheets-Sheet 3 United States Patent METHOD FOR THE COMMERCIAL RECTIFICA- TION OF A MIXTURE OF COMPONENTS George G. Crewson, Snyder, and Joseph R. Ryan, Williamsville, N. Y., assignors, by mesne assignments, to Food Machinery and Chemical Corporation, San Jose, Calif., a corporation of Delaware Application November 28, 1947, Serial No. 788,728

4 Claims. (Cl. 23207) This invention relates to a method for the commercial rectification of a mixture of two or more components which is capable of establishing solid and liquid phases in equilibrium with each other and with each phase containing such components but with the composition of one phase being proportionately higher in one component and lower in another component than the other phase and a change in the concentration of one of said components in both of said solid and liquid phases being accompanied by a change of both their respective melting and freezing points. In other words, i the invention relates to the rectification of a mixture of components capable of establishing solid and liquid phases in equilibrium with each other and in which mixture a change in temperature causes a change in the composition of each phase to restore equilibrium. Examples of such liquid mixtures are aqueous solutions of hydrogen peroxide; binary and ternary mixtures of homologues of pyridine, such as mixtures of 2,6-dirnethylpyridine, 4-methylpyridine and B-methylpyridine; and also solutions containing fatty acids and hydrocarbon solvents therefor, such as palmitic acid and benzene. i t t The invention will be particularly described with reference to the commercial production of hydrogen peroxide solutions having a concentration substantially in excess of 90%, such concentrations having been unattainable commercially heretofore.

Hydrogen peroxide in concentrations slightly above 90% is now produced in quantity by other processes. High concentration hydrogen peroxide is of importance because of the high energy output on decomposition and also because the decomposition yields active oxygenwhich can be effectively employed in specific applications. The effective energy output increases rapidly with increasing concentration but 90% is the approximate maximum limit of concentration of an aqueous solution of hydrogen peroxide with present commercial methods. While the present invention can also be used in producing hydrogen peroxide of lower concentration, it is particularly applicable to solutions above 90% concentration both because such desirable concentrations of hydrogen peroxide have heretofore been impossible to produce on a commercial scale and also because the present processes now in use are more economical in the production of hydrogen peroxide up to 90% strength. i 3

Accordingly, one of the principal objects of the present invention is the commercial production of a solution of hydrogen peroxide and water having a hydrogen peroxide concentration substantially higher than 90%.

Another objectfis the production of substantially anhydrous hydrogen peroxide on a commercial scale.

Another object is the production of hydrogen peroxide solutions of extreme purity withrespect to contaminants.

Another object is to provide such a method in which the amounts of contaminants present is progressively reduced as the concentration proceeds.

Another object is to provide such method which is of commercial capacities and can be applied either as a continuous or intermittent process.

Another object is to accomplish the rectification of aqueous solutions of hydrogen peroxide in a highly efllcient manner.

Another object is to provide such a method which is not critical in its operation.

Another object is to provide such a method which is safe, particularly with such liquids releasing great amounts of energy on decomposition such as highly concentrated hydrogen peroxide.

Other objects and advantages will appear from the following description and drawings in which:

Fig. l is a vertical section through apparatus for carrying out the present invention for rectification of a mixture wherein the solid phase is of higher density than the liquid phase.

Fig. 2 is a chart showing the temperature and concentration of the solid and liquid phases of higher concentrations of hydrogen peroxide at successive levels or zones in the apparatus shown in Fig. 1, this chart being arranged so that the zones are in horizontally alined relation to the apparatus illustrated in Fig. 1.

Fig. 3 is a vertical section through apparatus for carrying out the present invention for rectification of a mixture wherein the solid phase is of lower density than the liquid phase.

Fig. 4 is a chart showing the temperature and concentration of the solid and liquid phases of lower concentrations of hydrogen peroxide at successive levels or Zones in the apparatus shown in Fig. 3, this chart being arranged so that the zones are in horizontally alined relation to the apparatus illustrated in Fig. 3.

Fig. 5 isa graph of the freezing and melting point curves for solutions of hydrogen peroxide and water and in which temperature is plotted against concentration.

Hydrogen peroxide in concentrations up to approximately purity have been produced on a laboratory scale as shown by the article entitled Solid Solutions of Hydrogen Peroxide and Water, by P. A. Giguere and O. Maass, appearing in volume 18 of Canadian Journal of Research (1940), pages 66-73. These earlier investigations showed that hydrogen peroxide has the peculiar melting and freezing characteristics shown by the curves in the graph, Fig. 5. Referring particularly to the right hand side of this graph which is directed to concentrations of hydrogen peroxide above 60%, it will be noted that the melting point curve is separated from the freezing point curve. Most important, it will be noted that the melting point and freezing point of high concentration hydrogen peroxide increase with increasing concentrations of the peroxide. For concentrations represented by this right hand side the solid phase is heavier than the liquid phase and will settle downwardly through the liquid phase. With lower concentrations of hydrogen peroxide, represented by the left hand side of this graph, the solid phase is lighter than the liquid phase and will rise upwardly through the liquid phase.

Another factor determined by these earlier investigations was that with a hydrogen peroxide-water mixture at a given temperature a solid and liquid phase may exist in equilibrium with each other and with each phase containing both hydrogen peroxide and water but in different proportions in each of these phases. In such equilibrium and for concentrations above 60%, the concentration of the hydrogen peroxide in the solid phase or crystals is higher than the concentration of the hydrogen peroxide in the mother liquor before crystallization and the concentration of hydrogen peroxide in the liquid phase is lower than the concentration of hydrogen peroxide in the mother liquor before crystallization.

Previous investigators have produced small quantities of hydrogen peroxide solutions in excess of 90% concentration and approaching 100% concentration by successive crystallization, separation, remelting and recrystallization steps. Such a system, however, involves a number of stages of crystallization, separation of the solids from liquids, remelting the solids, and heat exchangers between solids and liquids, and is excessively complicated and entails too great installation and operating costs to be economically practicable.

The present invention utilizes the physical properties above mentioned in a single stage, continuous or intermittent and efficient process employing simple apparatus.

In the practice of the present invention feed liquor of a given concentration is admitted to a vessel and is chilled to establish solid and liquid phases and subjected to a changing environment in which the solid and liquid phases progressively increase in concentration in one cornponent of the feed liquor toward one end of the vessel as a result of seeking equilibrium under the conditions of the changing environment. The solid and liquid phases are not separated and the solid phase is moved in counterflow relation to the liquid phase so that heat exchange between the solid and liquid phases is effectively utilized. The concentrates, one of which is enriched in one of the components and the other of which is depleted in that component, are continuously or intermittently withdrawn from opposite ends of the vessel, the feed liquor being continuously or intermittently introduced at an intermediate concentration. The solid and liquid phases so moving in counterflow relation are subjected to a progressively changing temperature environment or temperature gradient which effects the increase in concentration of both phases. By regulation of the temperature gradient with both solid and liquid phases being simultaneously present, the desired concentrations of the end products or concentrates can be continuously produced.

In the apparatus shown in Fig. 1 for carrying out the invention with a solution wherein the solid phase is more dense than the liquid phase, the numeral represents an elevated cylindrical crystallizer which is shown as having a mother liquor return line 11 at its upper end and a feed line 12 connected with its conical bottom 13. This crystallizer 10 is shown as having a jacket or heat exchanger 14 and can be provided with a stirrer or agitator 15 of any suitable form. The jacket or heat exchanger 14 is provided with a supply line 16 and return line 18 for a cooling medium, a direct expanded refrigerant, such as Freon, being preferably employed.

The lower end of the conical bottom 13 of the crystallizer connects with the upper end of a vertical tube or leg 19. The crystallizer 10 and the tube or leg 19 thereby jointly form a vessel. This leg or tube 19 is surrounded by a jacket or heat exchanger 20 which is shown as supplied at its lower end with a heat exchange medium in the form of a heating medium through a supply line 21, a return line 22 being provided at the upper end of this jacket. The return line 22 is shown as discharging into a tank or reservoir 23 heated by a coil 24 having an inlet 25 and an outlet line 26. The line 21 connects with the bottom of the tank or reservoir 23 and recirculation of the liquid heating medium is provided by a pump 28.

A concentrate is withdrawn from the bottom of the leg or tube 19 through an overflow standpipe 29 which for ease of control preferably should extend approximately to the top of the tube or leg 19 but which can be of any height less than the liquid level in the crystallizer 10. A valve 27 is provided in the overflow standpipe 29.

A constant temperature of the liquid in the crystallizer 10 is maintained by a thermostat 30 immersed in this liquid and controlling a valve 31 in the cooling medium supply line 16'. The rate of flow of the heating medium through the jacket or heat exchanger 24) is controlled by a thermostat 32 in the heating medium return line 22 liquid phase is 82.5%.

controlling a valve 33 in the heating medium supply line 21. The heat input to the heating coil 24 is controlled by a thermostat 34 immersed in the concentrate leaving the lower extremity of the leg or tube 19 and controlling a valve 35 in the heat input line 25 to the coil 24. The jacket or heat exchanger 20 could, of course, be warmed by direct water flow but since in this particular example the temperature in this jacket or heat exchanger, for the production of highly concentrated hydrogen peroxide, will constantly be lower than 0 C. and since control oi the temperature gradient from the top to the bottom of the tube or leg 19 is desirable, the independent forced circulating system wherein both temperature and quantity of the heating medium can be controlled is preferred.

At the start of operation with the example illustrated in Figs. 1 and 2, the valve 27 in the overflow standpipe is closed and a solution of hydrogen peroxide and water at a concentration of hydrogen peroxide is admitted through the feed line 12, this solution flowing downwardly to fill the tube or leg 19 and rising to fill the crystallizer 10 to the overflow line 11. The solution in the crystallizer is then chilled to 20 C., this chilling being effected by heat exchange with the cooling medium passing through the heat exchanger or jacket 14 and under control of the thermostat 30. The solids formed in the crystallizer 10 from such cooling settle downwardly through the tube or leg 19. A vertically downwardly increasing temperature gradient is established in the solution contained in the tube or leg 19, this being accomplished by a heat exchange medium which in the present illustration is a heating medium, admitted at the lower end of the heat exchanger or jacket 20 from the supply line 21 and withdrawn from the upper end of this heat exchanger through the return line 22. Thus an increasing temperature gradient is established in the contents of the leg or tube 19 from the top to the bottom thereof, this gradient being under control of the thermostats 32 and 34. This tem perature gradient is shown as establishing a temperature of -3 C. at the bottom of the tube or leg 19 and progressively decreasing to 20 C. at the upper extremity thereof. It will be noted that this temperature of 20 C. established in the contents of the tube or leg 19 adjacent its upper extremity is the same as that to which the solution entering the crystallizer 10 is chilled. For convenience in explanation and understanding of the invention, the temperature gradient is divided into 1 intervals or eighteen zones in the table, .Fig. 2.

Referring to the graph, Fig. 5, it will be seen that the 90% hydrogen peroxide feed solution, chilled to -20 C. in zone 1 which comprises the crystallizer 10 and the upper extremity of the tube or leg 19, establishes solid and liquid phases, the solid phase being-of crystalline form. The hydrogen peroxide concentration of the solid phase is 93.2% and the hydrogen peroxide concentration of the This solid phase is appreciably heavier than the liquid phase and consequently settles out by gravity and moves downwardly into zone 2. Zone 2 is maintained at --19 C. whereas the crystals so settling into zone 2 melt at --20 C. Accordingly such crystals will melt and it will be seen that after a sutficient amount are so melted the 90% hydrogen peroxide solution in zone 2 will be replaced by a 93.2% hydrogen peroxide solution, this concentration corresponding to the composition of these crystals melted. However, referring to Fig. 5, at -l9 C. a solution in excess of 83.2% hydrogen peroxide concentration will freeze out a solid phase of 93.5% hydrogen peroxide concentration. Therefore when suflicient crystals have melted in zone 2 to have reduced the temperature therein to -20 C., additional solids will start to freeze out in zone 2 until the liquor at that point becomes of a concentration of 83.2% hydrogen peroxide and solids precipitated from such liquor are of 93.5% hydrogen peroxide concentration. It will be seen that since the solids formed in this zone 2 are of 93.5% concentration. whereas those coming to this zone from above are of 93.2% concentration, there must be an upflow of liquor of 83.2% concentration from zone 2 into zone 1 and since this liquor is of higherconcentration than the liquid phase established in zone 1 it will, on cooling, from 19 C. to 20 0, yield additional crystals to be added to those derived initially from the feed. In exactly a parallel manner, the crystals from zone 2, containing 93.5% hydrogen peroxide and at .19 C. settle to zone 3 where a temperature of -18 C. is established, and thus where only an equilibrium of 84% hydrogen peroxide in the liquid phase with 93.8% hydrogen peroxide in the solid phase can exist. Thus, in this same manner as for zone 2, the incoming crystals will be melted since this zone 3 is above the melting point for theircomposition, while new solids will be formed at 93.8% hydrogen peroxide con centration which settle downwardly, a liquor of 84% concentration flowing upwardly from zone 3 to be further depleted in its hydrogen peroxide content first in zone 2 and then in zone 1.

It will be seen that since more solids come tozone 2 than leave zone 2, and since the temperature of zone 2 is 1 higher than in zone 1, after the initial cooling to establish equilibrium conditions, some heat must be continuously added to zone 2 from the jacket 20. -Similarly, the total heat input to zone 3 is greater than the total heat output, so that heat must be added in this zone by means of the jacket 20.

For each successive lower zone the hydrocarbon peroxide concentration of both the liquid and solid phases becomes progressively greater, the crystals settling downwardly to melt in the higher temperature below their formation point and the residual liquor flowing upwardly and thus adding to the feed of the zone above. It will be seen that at any one point in the leg or tube 19 there are two feeds, one of solids settling from above, and one of liquor passing upwardly from below, both of which feeds are of higher hydrogen peroxide concentration thanthat corresponding to the freezing temperature at that point and hence will freeze out solids to settle downwardly and give residual liquor to flow upwardly. At any point in the leg or tube 19 the total heat content of the crystals from above and the liquor from below is less than the heat content of the residual liquor passing upwardly from that point plus that of the crystals settling down from that point, and heat ispreferably added in a uniform gradient throughout the length of the leg or tube 19..

This constant and progressive change in composition proceeds from the top to the bottom of the leg or tube 19 wherein in the assumed example the contents of the leg or tube are maintained at a controlled temperature of 3 C. At this point the feed is by means of crystals of 99% hydrogen peroxide settling from zone 17. Since there is no opportunity for crystals to settle out from the bottom of the leg or tube 19 and the temperature at that point is maintained at I-3 C., by means of a heat input, the liquid composition at that point corresponds to the liquid phase at -3 C. or 97.8% hydrogen peroxide concentration. When the valve 27 is opened this liquid phase in zone 18 is withdrawn as the end product enriched in hydrogen peroxide, this concentrateflowing out through the overflow standpipe 29.

The crystals constantly forming and constantly settling in the leg or tube 19 may provide a column. of crystals within this leg or tube. In any zone along this leg orttube the liquid and solid phases will have a composition corresponding to the table, Fig. 2, and hence the solid and liquid phases established throughout the heightof the leg or tube 19 are progressively richer in hydrogen peroxide content toward the bottom of the tube or leg. The rate of withdrawal of the concentrate through the overflow standpipe 29 is adjusted so that at all times the above continuous change in the compositions of the solid and liquid phases throughout the full length of the tube or leg 19 takes place, that is, the solid and liquid phases move relatively in counterflow relation to provide downwardly 6 moving crystals and upwardly moving liquor through a constantly maintainedtemperature gradient and in such movement the downwardly moving crystals are progressively enriched and the upwardly moving liquor is progressively depleted in hydrogen peroxide content.

The degree to which the leg or tube 19 in any given installation is packed with crystals is governed by the production rate and the concentration. limits both of the concentrate flowing out through the overflow standpipe 29 and the mother liquor flowing out through the motherliquor return line 11. With the leg or tube 10 compactly filled with crystals the slow percolation of liquor up through these crystals will increase the time and interface surfaces for phase interchange and hence the higher the product concentration required and the lower the mother liquor concentration desired, the more the leg or tube 19 tends to be compacted withcrystals and the limit of rectification obtainable with a given installation, regardless of the production rate, would be where the leg or tube 19 is entirely full of solids.

In the above, for simplicity of explanation, it has been stated that solids of a lower concentration will melt and new solids of a higher concentration will form. Actually, the present invention is essentially a rectification process and the actual phenomenon is an interchange of concentration within the crystal particles settling down from the crystallizer 10 with each crystal shrinking and releasing a part of its weight as a lowered concentration liquid and increasing its own hydrogen peroxide concentration. It is observed, in the practice of the present invention, that when equilibrium is reached, a crystal mass settling down from the crystallizer 10 does not melt as it settles down through the leg or tube 19 but shrinks in volume and increases in hydrogen peroxide concentration. The composition change therefore takes place. within the solid and liquid phases simultaneously and the practice of the invention is therefore essentially a liquid-solid phase rectification with enrichment of the solid phase and depletion of theliquid phase in hydrogen peroxide content.

The feed liquor can be introduced either into the crystallizer 10 as shown, or at any point along the tube or leg 19, the point of introduction of the feed liquor being determined by practical considerations such as blocking the system with large crystal formations localized at the inlet.

It will be seen that the invention can be practiced with mixtures of two or more components having the physical properties discussed above and where the solid phase is of lower density than the liquid phase. As an example of this application of the invention, the apparatus shown in Fig. 3 is described in conjunction with the rectification of a solution of hydrogen peroxide and water in which the hydrogen peroxide concentration is below 45%. Essentially, the apparatus shown in Fig. 3 is an inversion of the apparatus shown in Fig. 1, this being required be cause thesolid phase or the crystals rise, due to their lower density,.through the liquor within the vessel. Accordingly, the same reference numerals have been applied and are distinguished by the suifix a. The only modification of the apparatus shown in Fig. 3, other than the inversion of the apparatus as compared with Fig. l, is the relocation of the shaft of the agitator 15a and the provision of a foraminous screen 38 at the top of the tube or leg 19a, this screen restraining the further ascent of the solid phase or crystals in this tube or leg. For simplification, the apparatus for controlling the temperature of the cooling and heating media for the heat exchangers 14a and 29a, respectively, is not-illustrated.

In the operation of the apparatus shown in Fig. 3 it is assumed that a solution of hydrogen peroxide and water having a hydrogen peroxide concentration of 20% is to be rectified to provide a concentrate having a hydrogen peroxide concentration of 37.7% which is drawn oft through the outlet conduit 11a. For this purpose the leg or tube 19a, which is an upward extension of the crystallizenlOa, contains solid and liquid phases of the hydrogen peroxide and water solution which at the various-tempera= ture levels or zones indicated in Fig. 4, possess-the concentrations'in-hydro'gen peroxide set forth for these tem perature levels. The feed solution is introduced from the feed line- 12a through the conical part 13a into the crystallizer la-in which the solution is maintained at a temperature of -36 C. by a cooling medium such as a direct expanded refrigerant supplied to the heat exchanger or jacket 14a.

At this temperature a solid phase having a hydrogen peroxide content of 26.5% and a liquid phase having a hydrogen peroxide content of 37.7% are formed, these being the only compositions of -the phases which can exist in water-hydrogen peroxide solutions oflower concentrations, at this temperature of -37 C. as shown in the left hand side of the graph, Fig". 5. Since this solid phase is of lower density than this liquid phase, the crystals rise in the liquor contained in the-crystallizer a and enter the tube or leg 19a. In this tube or leg the temperature gradient indicated in Fig. 4 is maintained,'this temperature gradient being illustrated as progressively increasing from -36" C. in zone 1 at the bottom of the tube or leg to 2 C. at the top of this tube or leg, this temperature gradient being maintained by introducing a heating medium through the heat input line 21a at the upper end ofthe heat exchanger or jacket 29a surrounding the tube or leg 19a and withdrawing this heating medium through the outlet line 22a at the bottom of this-heat exchanger or jacket 29a.

On rising from each zone to the next higher zone each crystal encounters a higher temperature and a liquor having a hydrogen peroxide concentration'le'ss than that of the liquor in the preceding zone and hence releases a part of its hydrogen" peroxide to the surrounding liquor." At the same' time this enriched liquoris displaced downwardly and also freezes out additional crystals. Accordingly both the solid phase and the liquid phase decrease in hydrogen peroxide concentration toward zone 18 where the temperature of -2 C. is maintained and where the solid phase has a concentration of 0.8% hydrogen peroxide and the liquid phase has a concentration of 3.5% hydrogen peroxide, these being the only concentrations which can exist in these phases at this temperature. The dilute liquor having this concentration of 3.5% hydrogen peroxide is drawn off through the draw off line or conduit 29a'from zone 18, the crystals rising against the screen 38 melting to provide this liquor and to maintain equilibrium with the liquor in this zone. It will therefore be seen that the practice of the invention with lower concentrations of hydrogen peroxide as illustrated in Figs. 3 and 4 is the same as with the higher concentrations illustrated in- Figs. 1 and 2 except for those modifications necessitated by the fact that at lower concentrations the solid phase is of lower density than the liquid phase and "hence rises therein,

whereas at higher concentrations the solid phase is 'of higher density than the liquid phase and hence settles therein.

It will be seen that when operating on the left hand side of the graph as discussed in connection with Figs. 3 and 4, the freezing and melting points of hydrogen peroxide decrease withan increase in concentration of the hydrogen peroxide in both the solid and liquid phases, in contrast with operating on the right hand side of the graph,- as discussed in connection with Figs; '1 and 2, where the freezing and melting pointsof hydrogen peroxide increase with an increase in concentration of the hydrogenperoxide in both phases. Therefore the invention is generally applicable to such equilibrium solid-liquid phase mixtures in which a change in the temperature to alter the melting and freezing points-of both phases results in a change in the concentration of onecomponent in both phases.

From the foregoing it will beseen that the present invention provides continuous solid-liquid rectification on 'a commercial scale/and permits the eommercial product-ion offconcentrates, suchas solutions tat-hydrogen peroxide and water, which have heretofore been incapable of com-'- modifications can be made which will nevertheless fall within the scope-of this =-invention. For instance, mechanical means such as a conveyor could be provided to insure the counterfiow movement of the crystals relative to the liquor instead of employing the difference in density between the solid and liquid phases for this purpose.

l. The method of rectifying a solution of hydrogen peroxide and water wherein the hydrogen peroxide concentration is in excess of about 60%, which comprises chilling said solution to establish a solid phase, and moving said solid phase through a liquor of hydrogen peroxide and water having a progressively inc-reasing'concentration in hydrogen peroxide and a progressively increasing temperature whereby the concentration of said solid phase in hydrogen peroxide is progressively increased as a result of said solid phase seeking equilibrium with said liquor.

2. The method of rectifying a solution of hydrogen peroxide and water wherein the hydrogen peroxide concentration is in excess of about 60%, which comprises adjusting the temperature of a body of said solution to provide a temperature gradient along said body and to provide solid and-liquid phases with both of said phases progressively increasing in strength in hydrogen peroxide toward one end of said body and progressively increasing in strength'in water toward the other end of said body, feeding to said body a solution of hydrogen peroxide and water whereinthe hydrogen peroxide concentration is in excess of about 60-%, withdrawing from said one end of said body a coneentrate richer in hydrogen peroxide than said feed solution, and withdrawing from .said other end of said body a concentrate poorer in hydrogen peroxide than said feed solution.

3. The method of rectifying a solution of hydrogen peroxide and water wherein the' hydrogen peroxide concent-ration is in excess of about 60%, which comprises adjusting the temperature of a body of said solution to provide a temperature gradient along said body and to provide solid and liquid phases, relatively moving said phases'while in contact with each other toward opposite ends of said body whereby both of said phases progressively increase in strength in :hydrogen peroxide toward one end of said body and both of said phases progressively increase in strength in' water toward the other end of said body, feeding to said body a solution of hydrogen peroxide and water wherein the hydrogen peroxide concentration is in excess of about 60%, withdrawing from said one end of said body a concentrate richerin hy-' drogen peroxide than said feed solution, and withdrawing from said other end of said body a concentrate richer-in water than said feed solution.

4. The method of rectifying a solution of hydrogen peroxideand water wherein the hydrogen peroxide concentration is in excessof'about 60%, which comprises adjustingathe temperature of a body of said solution to provide a vertically downwardly increasing temperature gradient along said body and to provide solid and liquid phases with both of said phases progressively increasing in strength in hydrogen peroxide toward the lower end of saidbody and progressively, increasing in strength in water toward't-he upper-end of said body, feeding to said body a solution of hydrogen peroxide and water wherein therhydrogen peroxide concentration is in excess of about 60%, withdrawing from the lower part of said body a concentrate richer in hydrogen peroxide than'said feed solution, and'with'drawing from the upper part of said body'a concentrate richer in water than said feed solution, the withdrawal of said concentrates permitting said solid phase to descend bygravity through said liquid phase to etfect-relative movement between said phases whereby the progressive enrichment of said phases in hydrogenperoxide and water is maintained as a resuitof 'saidphases 9 seeking equilibrium under the conditicns of progressively 2,147,222 varying temperature and concentration. 2,307,130 2.427,042 References Cited in the file of this patent 2,540,977

UNITED STATES PATENTS 5 1,560,473 Howard Nov. 3, 1925 1,576,137 Johnson Mar. 9, 1926 1,863,751 Kipper June 21, 1932 Treub Feb. 14, 1939 Henry et a1. Jan. 5, 1943 Bowman Sept. 9, 1947 Arnold Feb. 6, 1951 OTHER REFERENCES Giguere et aL: Canadian Journal 6f Research, vol. 18, Sec. B, pp. 66-73 (1940). 

1. THE METHOD OF RECTIFYING A SOLUTION OF HYDROGEN PEROXIDE AND WATER WHEREIN THE HYDROGEN PEROXIDE CONCENTRATION IS IN EXCESS OF ABOUT 60*, WHICH COMPRISES CHILLING SAID SOLUTION TO ESTABLISH A SOLID PHASE, AND MOVING SAID SOLID PHASE THROUGH A LIQUOR OF HYDROGEN PEROXIDE AND WATER HAVING A PROGRESSIVELY INCREASING CONCENTRATION IN HYDROGEN PEROXIDE AND A PROGRESSIVELY INCREASING TEMPERATURE WHEREBY THE CONCENTRATION OF SAID SOLID PHASE IN HYDROGEN PEROXIDE IS PROGRESSIVELY INCREASED AS A RESULT OF SAID SOLID PHASE SEEKING EQUILBRIUM WITH SAID LIQUOR. 